FRYL

FRYL is a large evolutionarily conserved scaffold protein that operates as a transcriptional coactivator within developmental signaling complexes and as an organizer of NDR kinase signaling (PMID:28465505, PMID:38479391). In the nucleus, FRYL associates with the NOTCH1 activation complex alongside the PBAF remodeler and the histone demethylases LSD1 and PHF8 at Notch target genes (PMID:23022380), and acts within JAG/NOTCH signaling together with MAML2 to drive expression of soluble guanylyl cyclase (GUCY1A3/GUCY1B3) in arterial smooth muscle (PMID:28465505). FRYL was first identified as the COOH-terminal MLL fusion partner AF4p12 in t(4;11) leukemia, a fragment bearing a leucine zipper that confers transcriptional activation (PMID:16061630). Beyond transcription, FRYL functions as a Furry-family scaffold for NDR kinase, preferentially binding the activated/open conformation of NDR1 (PMID:29983373), and acts downstream of the Crumbs polarity complex where it binds Homer scaffolding proteins via their EVH1 domains and promotes liquid-like Homer condensates that selectively tune YAP and Wnt/β-catenin signaling output [PMID:bio_10.1101_2025.07.23.666266]. In vivo, FRYL is required for kidney tubular development and maintenance in mice (PMID:29409347) and for neuronal development in Drosophila (PMID:38479391), and heterozygous de novo loss-of-function variants cause a dominant neurodevelopmental disorder via haploinsufficiency (PMID:38479391).

1. 2005 Medium

   Established the first functional handle on FRYL by showing its C-terminal fragment, when fused to MLL in leukemia, carries intrinsic transcriptional activation potential—implicating the protein in gene activation.

   Evidence Cloning of the t(4;11) fusion transcript and Gal4-fusion transcriptional activation reporter assays

   PMID:16061630

   Open questions at the time

   • Activation domain assayed only as a Gal4 fusion, not in native FRYL context
   • No endogenous target genes identified
   • Does not address full-length FRYL function
2. 2012 Medium

   Placed FRYL within a defined nuclear machine by identifying it as a NOTCH1 activation-complex coactivator, linking it to chromatin remodeling and histone demethylation at Notch targets.

   Evidence Immunoaffinity purification of NOTCH1 nuclear partners with mass spectrometry in T-ALL cells

   PMID:23022380

   Open questions at the time

   • Interaction defined by co-purification, not direct binding mapping
   • Specific FRYL contribution to Notch target transcription not isolated
   • Single cell-type context
3. 2017 Medium

   Demonstrated a concrete physiological transcriptional output for FRYL: JAG/NOTCH-dependent control of soluble guanylyl cyclase expression in vascular smooth muscle, with relevance to hypertension.

   Evidence Gain/loss-of-function in vascular cells with sGC readout and expression analysis in hypertensive animal models

   PMID:28465505

   Open questions at the time

   • Direct DNA/promoter occupancy by FRYL not demonstrated
   • Mechanism of cooperation with MAML2 unresolved
   • Causal role in hypertension not established
4. 2018 Low

   Revealed a transcription-factor-complex partnership beyond Notch by isolating FRYL with the Ldb1-Lhx1 LIM-homeodomain complex.

   Evidence Tandem-affinity purification of Lhx1-associated proteins in Xenopus

   PMID:30375416

   Open questions at the time

   • Single TAP experiment with no functional follow-up for FRYL
   • Study focused on the FRY paralog
   • Direct vs indirect association unclear
5. 2018 Medium

   Established an essential developmental requirement for FRYL in mammalian organogenesis, localizing its function to renal tubular development and maintenance.

   Evidence Gene-trap null mouse with histopathology and tissue expression analysis

   PMID:29409347

   Open questions at the time

   • Molecular pathway connecting FRYL loss to tubular cell detachment unknown
   • Cause of perinatal lethality not defined
   • No link to transcriptional partners in kidney
6. 2018 Medium

   Connected FRYL to NDR kinase signaling as a Furry-family scaffold and defined conformational selectivity, showing it binds the activated/open state of NDR1.

   Evidence Crystal structure of NDR1 kinase domain with activation-segment mutagenesis and co-immunoprecipitation

   PMID:29983373

   Open questions at the time

   • FRYL binding inferred from NDR1 deletion-mutant co-IP, not direct interface mapping
   • Functional consequence of FRYL-NDR1 binding not tested
   • No cellular context for the interaction
7. 2019 Low

   Identified FRYL as a physical associate of NHLRC2 in macrophages, expanding its interaction landscape.

   Evidence Immunoprecipitation of NHLRC2 in macrophages

   PMID:31594818

   Open questions at the time

   • Single Co-IP as a secondary finding with no reciprocal validation
   • No functional consequence assessed for FRYL
   • Direct vs complex-mediated interaction unresolved
8. 2021 Medium

   Defined FRYL as a direct miR-1205 target overexpressed in prostate cancer, while excluding its role in miR-1205-driven neuroendocrine differentiation.

   Evidence miRNA target validation and FRYL knockdown in an NED induction assay in prostate cancer cells

   PMID:34386489

   Open questions at the time

   • Functional role of FRYL overexpression in prostate cancer not established
   • Negative NED result does not exclude other oncogenic functions
   • Mechanism of FRYL overexpression beyond miR-1205 unknown
9. 2024 High

   Established FRYL as a haploinsufficient disease gene by linking heterozygous de novo loss-of-function variants to a dominant neurodevelopmental disorder and functionally classifying variant pathogenicity in an in vivo model.

   Evidence Human genetics in 14 individuals plus Drosophila fry knockout, knockin variant modeling, mosaic clone analysis, and neuronal expression

   PMID:38479391

   Open questions at the time

   • Molecular pathway through which FRYL loss disrupts neurodevelopment not defined
   • Which signaling partner (NDR, Notch, Homer) mediates the phenotype unknown
   • Genotype-phenotype correlation across the variant spectrum incomplete
10. 2025 Medium

    Integrated FRYL into polarity-driven signaling by showing it scaffolds NDR kinase downstream of Crumbs, binds Homer EVH1 domains, and drives liquid-like Homer condensates that selectively partition YAP versus Wnt/β-catenin output.

    Evidence EVH1-domain pulldowns, YAP/Wnt functional assays, and live-cell imaging of phase-separated condensates (preprint)

    PMID:bio_10.1101_2025.07.23.666266

    Open questions at the time

    • Preprint, not yet peer-reviewed
    • Direct demonstration of FRYL in the Crumbs complex limited
    • Quantitative contribution of condensate topology to signaling not fully resolved

• It remains unknown how FRYL's distinct molecular roles—nuclear transcriptional coactivation, NDR kinase scaffolding, and Homer condensate organization—are integrated to produce its developmental and disease phenotypes.
• No unifying mechanism connecting transcriptional and cytoplasmic scaffolding functions
• Tissue-specific partner usage undefined
• No structural model of full-length FRYL or its scaffolding interfaces